by Dennis Overbye
The New York Times, August 12, 2013
This time, they say, Einstein might really be wrong.
A high-octane debate has broken out
among the world’s physicists
about what would happen
if you jumped into a black hole,
a fearsome gravitational monster
that can swallow matter, energy and even light.
You would die, of course, but how?
Crushed smaller than a dust mote
by monstrous gravity,
as astronomers and science fiction writers
have been telling us for decades?
Or flash-fried by a firewall of energy,
as an alarming new calculation seems to indicate?
This dire-sounding debate
has spawned a profusion of papers,
blog posts and workshops over the last year.
At stake is not Einstein’s reputation,
which is after all secure,
or even the efficacy of our iPhones,
but perhaps the basis
of his general theory of relativity,
the theory of gravity,
on which our understanding
of the universe is based.
Or some other fundamental
long-established principle of nature
might have to be abandoned,
but physicists don’t agree on which one,
and they have been flip-flopping
and changing positions almost weekly,
with no resolution in sight.
“I was a yo-yo on this,”
said one of the more prolific authors in the field,
Leonard Susskind of Stanford.
He paused and added,
“I haven’t changed my mind
in a few months now.”
Raphael Bousso,
a theorist at the University of California, Berkeley,
said, “I’ve never been so surprised.
I don’t know what to expect.”
You might wonder who cares,
especially if encountering
a black hole is not on your calendar.
But some of the basic tenets
of modern science
and of Einstein’s theory
are at stake in the “firewall paradox,”
as it is known.
“It points to something missing
in our understanding of gravity,”
said Joseph Polchinski,
of the Kavli Institute
for Theoretical Physics
in Santa Barbara, California,
one of the theorists
who set off this confusion.
Down this rabbit hole are many
of the jazzy magical mysteries
of modern physics: Black holes.
The shortcuts through space and time called wormholes.
Quantum entanglement,
also known as spooky action at a distance,
in which particles separated by light-years
can still instantaneously appear to remain connected.
The reward for going down this hole
could be a new understanding
of why we think we live in a universe
with space and time at all,
with suitably unpredictable consequences.
After all, if Einstein hadn’t been troubled
a century ago by logical inconsistencies
in the Newtonian universe,
we might not have GPS systems,
which rely on his theory of general relativity
to keep time, in our pockets today.
Falling Bodies
Black holes are the most
extreme predictions of Einstein’s theory,
which describes how matter and energy
warp the geometry of space and time
the way a heavy sleeper causes a mattress to sag.
Too much matter and energy in one place
could cause space to sag so far
that the matter inside it would disappear
as if behind a magician’s cloak,
collapsing endlessly to a point
of infinite density known as a singularity.
Einstein thought that idea was ridiculous
when it was pointed out to him at the time,
in 1916, but today astronomers agree
that the universe is speckled
with such dark monsters,
including beasts lurking
in the hearts of most galaxies
that are millions and billions of time
more massive than the Sun.
Many of them resulted
from the collapse of dead stars.
General relativity is based
on what Einstein later called
his “happiest thought,”
that a freely falling person
would not feel his weight.
It is known simply
as the equivalence principle;
it says that empty space
looks the same everywhere
and to everyone.
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